RADD 2501 WEB-RAD-TRAIN - Review Material for Interactions of Radiation with Matter

RADD 2501 WEB-RAD-TRAIN - Review Material for Interactions of Radiation with Matter

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Center for Radiological Research World Wide Web-Based Educational Program Review Topic 1 Contents Absorption of X rays Direct and Indirect Action Absorption of Neutrons DNA Strand Breaks Related Links Further Reading Quick Links Questions for this Topic Return to the RSNA Residents' Lounge Available Review Topics Interactions of Radiation with Matter Interactions of Radiation with Matter Printer-Friendly Format ABSORPTION OF X RAYS The process by which x-ray photons are absorbed depends on: the energy of the photons concerned and the chemical composition of the absorbing material. The Compton process dominates at high energies, characteristic of a cobalt-60 unit or a linear accelerator used for radiotherapy. In the Compton process: The photon interacts with what is usually referred to as a "free" electron, an electron whose binding energy is negligibly small compared with the photon energy. Part of the energy of the photon is given to the electron as kinetic energy; the photon, with whatever energy remains, continues on its way, deflected from its original path. In place of the incident photon there is a fast electron and a photon of reduced energy, which may go on to take part in further interactions. The net result is the production of a large number of fast electrons, many of which can ionize other atoms of the absorber, break vital chemical bonds, and initiate the change of events that ultimately is expressed as biological damage. Both the Compton process and photoelectric absorption occur for photon energies characteristic of diagnostic radiology, the former dominating at the higher end of the
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DNA Damage / Chromosomal Aberrations / Cellular Response Tissue Response to Radiation Factors Affecting Radiation Response Whole-Body Radiation Effects Fertility Radiation Carcinogenesis Radiation Cataractogenesis Effects on the Developing Embryo and Fetus Radiation Exposure to the Human Population Patient / Personal Exposure; Risk-Benefit Radiation Protection energy range (such as fluoroscopy) and the latter being most important at lower energies (such as mammography). Figure 1 The percentage of photon dose attributable to a given process as a function of photon energy is shown. In the process of photoelectric absorption: The x-ray photon interacts with a bound electron in, for example, the K, L, or M shell of an atom of the absorbing material. The photon gives up all of its energy to the electron; some is used to overcome the
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This note was uploaded on 11/22/2011 for the course RADD 2501 taught by Professor Sandyeverage during the Winter '11 term at Life Chiropractic College West.

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RADD 2501 WEB-RAD-TRAIN - Review Material for Interactions of Radiation with Matter

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